Living cationic polymerization of vinyl monomers by organoaluminium halides, 7. Effect of basicity and steric hindrance of added esters on the living polymerization of isobutyl vinyl ether with C2H5AlCl2

Abstract

AbstractThe living cationic polymerization of isobutyl vinyl ether (IBVE) with 1‐(isobutoxy)ethyl acetate (1)/C2H5AlCl2 as initiating system in hexane at +40°C in the presence of carboxylates was investigated in regard to the effect of the basicity and the steric hindrance of the added esters on the rate and living nature of the polymerization. The effect of the basicity was evaluated by use of four p‐substituted ethyl benzoates (XC6H4COOC2H5; X: CH3O, CH3, H, Cl). Despite of the difference in basicity, all the benzoates gave living polymers with narrow molecular‐weight distributions (ratios of weight‐ to number‐average molecular weights Mw/Mn ≤ 1,1), whereas the polymerization rate depends on the p‐substituents as follows: CH3O < CH3 < H < Cl. Another series of experiments showed that the steric environment around the carbonyl group also affects the polymerization rate. Namely, using carboxylates with various carbonyl substituents (RCOOCH3; R: CH3, C2H5, (CH3)2CH, (CH3)3C), the polymerization rate increases with increasing bulkiness of the substituent R in the order: (CH3)3C > (CH3)2CH > C2H5 > CH3. These electronic and steric effects are consistent with the stabilization of the carbocation by the nucleophilic interaction of added bases. Fast living polymerization of IBVE can be obtained using the initiating system 1/C2H5AlCl2 in the presence of methyl chloroacetate, an ester with a strongly electron‐withdrawing group.